The adoption period has begun for the two dozen cats and kittens dumped at the Marin Humane Society before sunrise last week.

Spokeswoman Lisa Bloch said the legally mandated seven-day "stray hold" waiting period has expired, allowing the shelter to prepare the cats for adoption. The waiting period exists in case people come in to claim lost animals.

Shelter officials suspect the black-and-white "tuxedo" cats, which were not spayed or neutered, were dumped by the same people who have abandoned more than 100 cats at the shelter in three other drops over the past 18 months. They have not been identified, Bloch said.

The unexpected influx of cats brought the existing shelter population to nearly 200, far more than normal levels. As a result, the shelter waived the $100-125 cat adoption fees for the rest of August in the hopes of reducing the backlog. The cost of preparing cats for adoption is about $500.

The shelter has been vaccinating, microchipping and spaying or neutering the cats in preparation for the end of the waiting period.